The present invention generally relates to an electrographic process and more particularly, to a developing method for developing an electrostatic latent image carried on a surface of an electrostatic latent image support member.
Generally, for developing an electrostatic latent image formed on a photosensitive member into a visible image, a two-component developing material prepared by mixing carrier of iron particles, ferrite powder, etc. with toner has been widely employed for actual applications. The developing material of the above described type is employed in the developing by mixing and stirring the carrier particles and toner particles for electrostatic attraction therebetween through triboelectric charging prior to being supplied onto the electrostatic latent image (based, for example, on a cascade system, magnetic brush system, or the like).
In the above case, only the toner of the above developing material electrostatically adheres to the image portion of the electrostatic latent image so as to be consumed, and therefore, it is necessary to properly replenish toner corresponding to the consumption into the developing material. During the above replenishment, the supplied toner is required to be rapidly electrically charged to a predetermined amount of charge through contact thereof with the carrier, because dusting of the toner or scattering thereof takes place due to delay in the rising charge, thus resulting in soiling inside and outside the copying apparatus.
Therefore, in order to accelerate the rising electric charge of the toner, it there has conventionally been proposed to improve a developing material stirring mechanism, etc., but in the case where the amount of replenishment per unit of time is increased (particularly as in a high speed copying apparatus), it is difficult to achieve a sufficiently rapid rising charge.
Meanwhile, for solving the problem described above, it may be considered to triboelectrically charge the toner preliminarily to a predetermined polarity before the replenishment, and the present inventors have employed, on a trial basis, a method in which particles triboelectrically charged to a polarity opposite to that of the toner are preliminarily mixed into the replenishing toner, the result of which, however, has undesirably led to an increase in the dusting of toner. The above inconvenience is assumed to be attributable to the fact that within the developing tank, the toner and the particles added thereto tend to be triboelectrically charged to an opposite polarity with respect to each other through contact with the carrier, and consequently, the charging characteristics of the carrier become unstable, with a particular reduction in the charge amount of the carrier, thus making it impossible for the carrier to sufficiently hold the toner.